gcc.1

这是完整的gcc源代码

.TH GCC 1 "28 November 1990" "Version 1.40"
.de BP
.sp
.ti -.2i
\(**
..
.SH NAME
gcc \- GNU project C Compiler
.SH SYNOPSIS
.B gcc
[ options ] files
.SH WARNING
This man page is an extract of the documentation of the
.I GNU C compiler
and is limited to the meaning of the options.
.B It is not kept up to date.
If you want to be certain of the information
below, check it in the manual "Using and Porting GCC".  Refer to the Info file
.B gcc.info
or the DVI file
.B gcc.dvi
which are made from the Texinfo source file
.BR gcc.texinfo .
.SH DESCRIPTION
The
.I GNU C compiler
uses a command syntax much like the Unix C compiler.
The
.I gcc
program accepts options and file names as operands.
Multiple single-letter options may
.I not
be grouped:
.B \-dr
is very different from
.BR "\-d \-r" .
.P
When you invoke GNU CC, it normally does preprocessing, compilation,
assembly and linking.
File names which end in
.B .c
are taken as C source to be preprocessed and compiled;
file names ending in
.B .i
are taken as preprocessor output to be compiled;
compiler output files plus any input files with names ending in
.B .s
are assembled;
then the resulting object files, plus any other input files,
are linked together to produce an executable.
.P
Command options allow you to stop this process at an intermediate stage.
For example, the 
.B \-c
option says not to run the linker.
Then the output consists of object files output by the assembler.
.P
Other command options are passed on to one stage of processing.
Some options control the preprocessor and others the compiler itself.
Yet other options control the assembler and linker;
these are not documented here, but you rarely need to use any of them.
.SH OPTIONS
Here are the options to control the overall compilation process,
including those that say whether to link, whether to assemble, and so on.
.TP
.BI \-o " file"
Place output in file
.IR file .
This applies regardless to whatever sort of output is being produced,
whether it be an executable file, an object file,
an assembler file or preprocessed C code.
.sp
If 
.B \-o
is not specified, the default is to put an executable file in
.BR a.out ,
the object file
.IB source .c
in
.IB source .o\fR,
an assembler file in
.IB source .s\fR,
and preprocessed C on standard output.
.TP
.B \-c
Compile or assemble the source files, but do not link.
Produce object files with names made by replacing
.B .c
or
.B .s
with
.B .o
at the end of the input file names.
Do nothing at all for object files specified as input.
.TP
.B \-S
Compile into assembler code but do not assemble.
The assembler output file name is made by replacing
.B .c
with
.B .s
at the end of the input file name.
Do nothing at all for assembler source files or
object files specified as input.
.TP
.B \-E
Run only the C preprocessor.
Preprocess all the C source files specified and output
the results to standard output.
.TP
.B \-v
Compiler driver program prints the commands it executes as it runs
the preprocessor, compiler proper, assembler and linker.
Some of these are directed to print their own version numbers.
.TP
.B \-pipe
Use pipes rather than temporary files for communication between the
various stages of compilation.
This fails to work on some systems where the assembler is unable
to read from a pipe; but the GNU assembler has no trouble.
.TP
.BI \-B prefix
Compiler driver program tries
.I prefix
as a prefix for each program it tries to run.
These programs are
.IR cpp ,
.IR cc1 ,
.I as
and
.IR ld .
.sp
For each subprogram to be run, the compiler driver first tries the
.B \-B
prefix, if any.
If that name is not found, or if
.B \-B
was not specified, the driver tries two standard prefixes, which are
.B /usr/lib/gcc-
and
.BR /usr/local/lib/gcc- .
If neither of those results in a file name that is found, the
unmodified program name is searched for using the directories
specified in your
.B PATH
environment variable.
.sp
The run-time support file
.B gnulib
is also searched for using the
.B \-B
prefix, if needed.
If it is not found there, the two standard prefixes above
are tried, and that is all.
The file is left out of the link if it is not found by those means.
Most of the time, on most machines, you can do without it.
.sp
You can get a similar result from the environment variable
.BR GCC_EXEC_PREFIX ;
if it is defined, its value is used as a prefix in the same way.
If both the
.B \-B
option and the
.B GCC_EXEC_PREFIX
variable are present, the
.B \-B
option is used first and the environment variable value second.
.TP
.BI -b prefix
The argument
.I prefix
is used as a second prefix for the compiler executables and libraries.
This prefix is optional: the compiler tries each file first with it,
then without it.
This prefix follows the prefix specified with
.B \-B
or the default prefixes.
.sp
Thus,
.B \-bvax- \-Bcc/
in the presence of environment variable
.B GCC_EXEC_PREFIX
with definition
.B /u/foo/
causes GNU CC to try the following file names for the preprocessor executable:
.sp
	\fBcc/vax-cpp
.br
	cc/cpp
.br
	/u/foo/vax-cpp
.br
	/u/foo/cpp
.br
	/usr/local/lib/gcc-vax-cpp
.br
	/usr/local/lib/gcc-cpp
.br
	/usr/lib/gcc-vax-cpp
.br
	/usr/lib/gcc-cpp\fR
.P
These options control the details of C compilation itself.
.TP
.B \-ansi
Support all ANSI standard C programs.
.sp
This turns off certain features of GNU C that are incompatible with
ANSI C, such as the
.BR asm ,
.B inline
and
.B typeof
keywords, and predefined macros such as
.B unix
and
.B vax
that identify the type of system you are using.
It also enables the undesirable and rarely used ANSI trigraph feature.
.sp
The alternate keywords
.BR __asm__ ,
.B __inline__
and
.B __typeof__
continue to work despite
.BR \-ansi .
You would not want to use them in an ANSI C program, of course,
but it useful to put them in header files that might be included
in compilations done with
.BR \-ansi .
Alternate predefined macros such as
.B __unix__
and
.B __vax__
are also available, with or without
.BR \-ansi .
.sp
The
.B \-ansi
option does not cause non-ANSI programs to be rejected gratuitously.
For that,
.B \-pedantic
is required in addition to
.BR \-ansi .
.sp
The macro 
.B __STRICT_ANSI__
is predefined when the
.B \-ansi
option is used.
Some header files may notice this macro and refrain from declaring
certain functions or defining certain macros that the ANSI standard
doesn't call for; this is to avoid interfering with any programs
that might use these names for other things.
.TP
.B \-traditional
Attempt to support some aspects of traditional C compilers.
Specifically:
.BP
All
.B extern
declarations take effect globally even if they are
written inside of a function definition.
This includes implicit declarations of functions.
.BP
The keywords
.BR typeof ,
.BR inline ,
.BR signed ,
.B const
and
.B volatile
are not recognized.
.BP
Comparisons between pointers and integers are always allowed.
.BP
Integer types
.B "unsigned short"
and
.B "unsigned char"
promote to
.BR "unsigned int" .
.BP
Out-of-range floating point literals are not an error.
.BP
All automatic variables not declared
.B register
are preserved by
.IR longjmp (3C).
Ordinarily, GNU C follows ANSI C: automatic variables not declared
.B volatile
may be clobbered.
.BP
In the preprocessor, comments convert to nothing at all,
rather than to a space.
This allows traditional token concatenation.
.BP
In the preprocessor, macro arguments are recognized within string
constants in a macro definition (and their values are stringified, though
without additional quote marks, when they appear in such a context).
The preprocessor always considers a string constant to end at a newline.
.BP
The predefined macro
.B __STDC__
is not defined when you use
.BR \-traditional ,
but
.B __GNUC__
is (since the GNU extensions which
.B __GNUC__
indicates are not affected by
.BR \-traditional ).
If you need to write header files that work differently depending on whether
.B \-traditional
is in use, by testing both of these predefined macros you can distinguish
four situations: GNU C, traditional GNU C, other ANSI C compilers, and
other old C compilers.
.TP
.B \-O
Optimize.
Optimizing compilation takes somewhat more time,
and a lot more memory for a large function.
.sp
Without
.BR \-O ,
the compiler's goal is to reduce the cost of compilation and
to make debugging produce the expected results.
Statements are independent: if you stop the program with a breakpoint
between statements, you can then assign a new value to any variable or
change the program counter to any other statement in the function and
get exactly the results you would expect from the source code.
.sp
Without
.BR \-O ,
only variables declared
.B register
are allocated in registers.
The resulting compiled code is a little worse than produced by PCC without
.BR \-O .
.sp
With
.BR \-O ,
the compiler tries to reduce code size and execution time.
.sp
Some of the
.B \-f
options described below turn specific kinds of optimization on or off.
.TP
.B \-g
Produce debugging information in the operating system's
native format (for DBX or SDB).
GDB also can work with this debugging information.
.sp
Unlike most other C compilers, GNU CC allows you to use
.B \-g
with
.BR \-O .
The shortcuts taken by optimized code may occasionally
produce surprising results: some variables you declared may not exist
at all; flow of control may briefly move where you did not expect it;
some statements may not be executed because they compute constant
results or their values were already at hand; some statements may
execute in different places because they were moved out of loops.
Nevertheless it proves possible to debug optimized output.
This makes it reasonable to use the optimizer for programs
that might have bugs.
.TP
.B \-w
Inhibit all warning messages.
.TP
.B \-W
Print extra warning messages for these events:
.BP
An automatic variable is used without first being initialized.
.sp
These warnings are possible only in optimizing compilation,
because they require data flow information that is computed only
when optimizing.
If you don't specify
.BR \-O ,
you simply won't get these warnings.
.sp
These warnings occur only for variables that are candidates for
register allocation.
Therefore, they do not occur for a variable that is declared
.BR volatile ,
or whose address is taken, or whose size is other than 1, 2, 4 or 8 bytes.
Also, they do not occur for structures, unions or arrays, even when
they are in registers.
.sp
Note that there may be no warning about a variable that is used only
to compute a value that itself is never used, because such
computations may be deleted by data flow analysis before the warnings
are printed.
.sp
These warnings are made optional because GNU CC is not smart
enough to see all the reasons why the code might be correct
despite appearing to have an error.
Here is one example of how this can happen:
.sp
	{
.br
	\ \ int x;
.br
	\ \ switch (y)
.br
	\ \ \ \ {
.br
	\ \ \ \ case 1: x = 1;
.br
	\ \ \ \ \ \ break;
.br
	\ \ \ \ case 2: x = 4;
.br
	\ \ \ \ \ \ break;
.br
	\ \ \ \ case 3: x = 5;
.br
	\ \ \ \ }
.br
	\ \ foo (x);
.br
	}
.sp
If the value of 
.I y
is always 1, 2 or 3, then
.I x
is always initialized, but GNU CC doesn't know this.
Here is another common case:
.sp
	{
.br
	\ \ int save_y;
.br
	\ \ if (change_y) save_y = y, y = new_y;